Add backend foundation: database models, security, and mail processing service

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

backend/app/core/database.py

@@ -0,0 +1,40 @@
+"""
+Database configuration and session management.
+"""
+from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession, async_sessionmaker
+from sqlalchemy.orm import declarative_base
+from app.core.config import settings
+
+# Create async engine
+engine = create_async_engine(
+    settings.DATABASE_URL,
+    echo=settings.DEBUG,
+    pool_size=settings.DATABASE_POOL_SIZE,
+    max_overflow=settings.DATABASE_MAX_OVERFLOW,
+    pool_pre_ping=True,
+)
+
+# Create async session factory
+async_session_maker = async_sessionmaker(
+    engine,
+    class_=AsyncSession,
+    expire_on_commit=False,
+    autocommit=False,
+    autoflush=False,
+)
+
+# Base class for models
+Base = declarative_base()
+
+
+async def get_db() -> AsyncSession:
+    """Dependency for getting async database session"""
+    async with async_session_maker() as session:
+        try:
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise
+        finally:
+            await session.close()